Conventional methods for producing solid form microcapsules can be generally classified into chemical methods such as an interfacial polymerization method and an in-situ polymerization method; physical/chemical methods such as a coacervation method, an interfacial precipitation method, a liquid phase drying method and a liquid phase film hardening method (orifice method); and mechanical methods such as a spray drying method, a spray cooling method, a dry blending method and a membrane emulsification method. Among these, as methods for producing microcapsules in which a hydrophilic substance is encapsulated, techniques such as an interfacial polymerization method, an in-situ polymerization method, a liquid phase drying method, an liquid phase film hardening method (orifice method), a spray drying method, a spray cooling method, a membrane emulsification method and the like have been known.
Patent Document 1 discloses an example of capsulation of a core substance that is easily affected from an acid, moisture or heat, by a liquid phase film hardening method (orifice method) using a multinozzle. Since the capsules produced by this method will have a mononuclear type capsule structure, it is advantageous in capability of increasing the content of the core substance, and availability of capsules having a seamless structure, and the like. However, the produced capsules often have a large particle size with a diameter in the order of several mm, and the degree of freedom of selectable particle size range is low, leading to a problem of difficulty in application and development to a variety of fields such as use as soft capsules, tablets, and the like.
On the other hand, known microcapsules produced using an emulsion include, for example, microcapsules having an S/O type or W/O type structure.
S/O type or W/O type microcapsules can be applied to a large variety of use such as foods, trophic foods, specified health foods, medical drugs, cosmetics, feeds, pesticides and the like by enclosing a substance that contains a useful component in a liquid or solid form oil phase. In production of microcapsules of such applications, there exist demands for improvement of yield in producing the capsules, increase in the content of the enclosed substance, a wide range of choice of the capsule particle size, and control of release pattern of the core substance and the like in light of DDS.
Furthermore, in the case of W/O type solid form microcapsules, there arise problems of storage stability of the microcapsules such as putrefaction of the moisture encapsulated in the microcapsule, hydrolysis of the bioactive substance dissolved in the moisture, and the like. Additionally, in regard to the method for production, for example, when W/O type solid form microcapsules are obtained after forming a W/O/W emulsion in the liquid phase, the aqueous phase containing a bioactive substance polydispersed in an oil phase likely generates a driving force to the external side of the droplets dispersed in the oil phase due to the surface tension. Thus, this driving force promotes leakage of the bioactive substance to the external aqueous phase, and may lead to decrease in encapsulation yield of the bioactive substance in the microcapsules.
To the contrary, in the case of S/O type microcapsules, since a bioactive substance in a solid form is polydispersed in the microcapsules, the moisture content is comparatively low, and putrefaction or degradation of the bioactive substance less likely occurs. In addition, even though the bioactive substance in a solid form polydispersed in the oil phase forms oil droplets, they would be less subject to a great driving force that results from the surface tension.
However, as a method for production of S/O type microcapsules which has been known heretofore, for example, a liquid phase drying method (Patent Document 2) is exemplified: In this method, organic solvents that are deleterious to the human body such as halogenated hydrocarbons or ethers are used in the production process of the microcapsules; therefore, application to usage for foods is difficult. Moreover, the microcapsules produced by the liquid phase drying method have problems of physical fine pores which are likely to be formed on the capsule film, and leakage of the core substance likely to occur toward outside the membrane, and the like, contrary to an advantage that utilization as sustained release microcapsules is enabled.
Additionally, an example of producing S/O type microcapsules by membrane emulsification utilizing a solid fat as a shell material to prepare a fine W/O/W emulsion, followed by freeze-drying was proposed (Patent Document 3). However, increase in the content of the core substance is difficult, and problems of pressure loss and clogging that may occur during membrane emulsification, as well as durability of the membrane and the like are involved. Therefore it has been difficult to ensure a production amount suited for industrial production.
Meanwhile, glutathione is a tripeptide composed of three amino acids of glutamic acid, glycine and cysteine, and is an antioxidative substance which widely distributes in tissues of living bodies. Glutathione has been found to have an effect of detoxicating detrimental substances that may cause variation or deterioration of cellular functions in a body to strengthen liver functions. Additionally, glutathione serves in suppressing production of lipid peroxide which has been considered to bring about aging and malignant transformation of cells, or protecting a body from lipid peroxide already produced. In these regards, glutathione is reportedly effective in preventing, in general, chronic hepatic diseases such as alcoholic fatty liver, as well as corneal injury, skin disorder, medicinal poisoning, gestosis, leukopenia due to radiation or anticancer agent and the like, and also referred to as having an efficacious action on stress.
So far, attempts for permitting oral ingestion of glutathione have been made by admixing in a food or a supplement; however, achieving sufficient pharmacologic effects is reportedly impossible in many cases due to degradation by digestive enzymes and low absorptivity from the gastrointestinal tract. As an effective administration form of glutathione, intravenous injection has been generally employed.
Moreover, according to Patent Document 4, a liposome preparation enclosing glutathione was investigated in an attempt to improve oral absorptivity; however, liposome is accompanied by a problem of shelf life of the preparation.
Typical imidazole dipeptides include anserine, carnosine and the like which are dipeptides in which α-alanine and L-histidine or a derivative thereof are bonded. Of these, anserine is a substance included in a large quantity in fishes such as skipjack, tuna, salmon and shark as well as in the muscle of chicken. The imidazole dipeptides such as anserine have a high buffer capacity in a physiological pH range and have been verified to be effective in maintaining physical capabilities and resisting against fatigue by suppressing lowering of muscular pH due to lactate accumulation and the like, and reportedly have functions such as an uric acid level suppressing action, an active oxygen scavenging action, an blood pressure lowering action and an anti-inflammatory action.
With respect to formulation of the imidazole dipeptides, they are generally prepared by tableting or filling in a hard capsule. However, since degradation by digestive enzymes can occur in oral ingestion, carrying out a treatment such as protection of the preparation from gastric acid and the like is believed to be necessary in order to achieve the pharmacologic effects efficiently.
Additionally, although bulk powders of anserine are purified from fishes, in general, by steps of extraction, desalting, drying and the like. Thus resulting anserine bulk powders are known to have a low bulk density, and inferior powder flow characteristics. They are often mixed usually with an excipient such as dextrin to obtain the preparation. Accordingly, preparation of bulk powders containing anserine at a high content has been recognized as being difficult. Moreover, the anserine bulk powders derived from fishes often have remaining unpleasant odor constituents peculiar to fishes, which may raise problems such as restraints in oral ingestion, and the like.
Patent Document 1: JP No. 3,102,990
Patent Document 2: JP-A No. 2003-252751
Patent Document 3: JP-A No. 2004-8015
Patent Document 4: United States Patent Application, Publication No. 2006/0099244